1. Field of the Invention
The present invention is directed to a rotary combustor useful in a waste disposal system for the combustion of solid waste materials and, more particularly, to an improved rotary combustor having a device for removing material accumulated on a bottom surface of a windbox.
2. Description of the Related Art
Waste disposal systems employing rotary combustors for the combustion of waste materials have long been known. For example, numerous types of waste disposal combustion systems for solid waste materials have been employed for the disposal of municipal waste. Useful types of such waste disposal systems are described in U.S. Pat. Nos. 3,822,651, 4,615,283 and 4,782,769. These types of waste disposal combustion systems utilize a rotary combustor formed by plurality of longitudinally extending pipes secured together to form a cylindrical combustion barrel defining a combustion chamber therein. The pipes are connected together by webs having openings therein for entry of combustion air into the combustion barrel. The pipes are adapted to accommodate the flow of water therethrough to cool the walls of the combustion barrel and produce steam. Air is charged to the combustion barrel through various means such as windboxes and combustion gases from the unit passed to a boiler or furnace for further production of steam. Ash from the combustion material falls out of the outlet end of the combustor into an ash receiving chamber. These types of waste disposal combustion systems have been found very useful in waste disposal while providing revenue through generation of steam and electric power.
While waste disposal systems employing rotary combustors as described above are capable of burning most types of combustible waste, certain problems arise when the waste includes matter such as low melting temperature metals, particularly, those used in beverage containers, foil, disposable trays, etc., which contain aluminum. Aluminum melts at a temperature lower than the operating temperature in the combustion barrel and therefore the aluminum turns into liquid and flows through the combustion air openings in the combustion barrel and down into the windboxes under the barrel. The liquid or molten metal then tends to accumulate on the bottom wall of each windbox where it cools off rapidly due to the cooler temperatures therein and eventually creates a thick sheet of material on the bottom of each windbox. Periodic removal of this layer or sheet is necessary in order to continue efficient operation of the combustor.
One method current used is a manual technique that requires a partial outage of the combustor during removal. During the removal period, the combustor power level is reduced and carbon monoxide (CO) control is stopped. This situation results in a loss of availability and poor emissions control.
Another method which has been developed which does not require a partial outage of the combustor is that described in U.S. Pat. No. 4,782,769 which employs a heated surface at the bottom of the windbox to keep any molten metal such as aluminum in a liquid state wherein it may be drained out of the windbox through a heated pipe. While this method and apparatus has proved useful, a need still exists for other ways of removing material such as aluminum which collects in the bottom of the windboxes while the combustor is still at full power.